BG Group (deal value - $70.1 billion)

In February 2016, British BG Group became part of the British-Dutch oil group Royal Dutch Shell. The merged corporation is the second-largest private oil and gas company in terms of capitalization ($177 billion). Only the American ExxonMobil worth $337 billion is ahead. After the deal had been finalized, the shareholders of BG Group received 19% of the joint company's shares.

TNK-BP (deal value - $55.4 billion)

In October 2012, Rosneft and British Petroleum (BP) agreed on the acquisition of a 50% BP's share in TNK-BP by the Russian company. The cash expenditure amounted to $17.12 billion. As a result, Rosneft paid $16.65 billion to the British oil and gas company.

Petrobras (deal value - $42.6 billion)

In 2010, Brazil’s oil and gas assets were the subject of a major transaction in the oil sector. Petrobras placed 2.4 billion ordinary shares and 1.87 billion preferred shares totalling $69.9 billion. Experts estimated that was the largest amount of funds raised by one placement. Nothing like this had ever happened before in the stock market.

Burlington Resources (deal value - $35.6 billion)

In 2015, ConocoPhillips signed an agreement to acquire Burlington Resources, an American oil and gas company, for $35.6 billion. Following the signing of the definitive agreement, Burlington Resources shareholders received $46.50 in cash and 0.7214 shares of ConocoPhillips common stock for each Burlington Resources share they owned.

Baker Hughes (deal value - $35.5 billion)

In 2014, two global oilfield services giants, Halliburton and Baker Hughes, agreed on an asset swap. The negotiations lasted several weeks. Under the original contract, Halliburton was supposed to take over Baker Hughes, paying $78.62 for each Baker Hughes share. However, later, Halliburton and Baker Hughes scrapped a $28 billion merger deal.

Hydro Nordisk (deal value - $35.5 billion)

In 2006, two Norwegian oil and gas companies, Statoil and Hydro, agreed to merge their oil and gas operations. The newly created firm has become one of the biggest offshore oil and gas companies in the world.

XTO Energy (deal value - $24.9 billion)

In 2009, ExxonMobil acquired XTO Energy, thereby becoming the leading natural gas producer in the United States. The merger enabled ExxonMobil to participate in the most successful oil and gas projects. The deal was implemented through the exchange of shares. Nothing like this has happened in the company for more than ten years, that is, since the merger between Exxon and Mobil.

Phillips 66 (deal value - $20.7 billion)

In 2012, the Board of Directors of ConocoPhillips approved the decision to split the company into two smaller energy companies, ConocoPhillips and Phillips 66. ConocoPhillips is currently engaged in geological exploration and production of hydrocarbons. The second company, Phillips 66, specializes in oil refining, marketing, and petrochemicals.

Cenovus Energy (deal value - $18.8 billion)

In 2009, Cenovus Energy, the largest oil and gas producer, split into two enterprises. One of them specializes in natural gas, while the other addresses issues of the joint oil company. The firm engaged in natural gas production is called EnCana Corp.

Petro-Canada (deal value - $17.8 billion)

In 2009, Suncor merged with Petro-Canada. This made it fifth largest energy company in the United States. The deal made it possible to reduce annual costs by 1 billion Canadian dollars.